This invention relates to improvements in cordless, battery operated pens for inputting data and information into a tablet computer. More specifically, the invention relates to a pen having improved circuitry for preventing accidental discharge of the pen battery.
Cordless and untethered magnetic pens are known in the prior art, which are used to input data into a tablet computer. One such pen emits a modulated radio frequency (RF) field that is received and demodulated by electronics with the tablet computer. The detected field is used by the system software to determine the location of the pen with respect to a magnetic grid thereby allowing a user to input data into the computer. The pen includes a normally closed switch and an oscillator that oscillates at two different frequencies dependent on whether the switch is open or closed, and the oscillator controls the frequency of the RF field emitted by the pen. The switch is located at the tip of the pen and is sometimes referred to as a "tip switch".
When the tip of the pen is moved into contact with an object such as the magnetic grid, two events occur. First, the switch opens and an oscillator is turned on to operate at a frequency signifying that the pen is in contact with the grid. Second, a time out circuit is enabled or engaged to limit the time that battery power is applied to the oscillator. This time limit is reset each time the pen tip comes into contact with the grid. However, if the tip switch is compressed in a fixed position, such as is possible when the pen is stored in a user's pocket, a drawer, a briefcase, etc., the time out circuit is rendered ineffective and the battery applies continuous power to the oscillator. This action causes the battery to be completely discharged in a short period. Without a recharge mechanism, the discharged battery must be replaced.